Method for production of involute gear tooth flanks

ABSTRACT

A method is disclosed in which only one working point or machining point on a machining tool, which in general can comprise a grinding wheel or disc, is in machining contact with a workpiece such as a gear blank during a machining operation. The position of this single working or machining point can be selectively chosen within a machining region of the grinding wheel or disk and can be prescribed to lie in a zone of fixed or variable radius of the grinding wheel or disk. This is achieved through at least one feed motion, in general a feed motion of the grinding wheel or disc, effected in addition to feed motions known per se in machining processes performed essentially according to the indexing generating method. This means that the machining contact point between the grinding wheel or disk and the gear blank does not wander on the grinding wheel or disk in correspondence with the generating feed motions but can be confined to a predeterminate region. It is nevertheless possible to displace this working or machining point in an orderly and programmed manner, i.e. under control, to optimally exploit the machining tool. In accordance with the method, the machining point can be guided along different types of machining lines, for example along lines which at least approximate tooth flank generatrices or along lines which at least approximate tooth traces or flank lines and which may be helical.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to the commonly assigned co-pending U.S.Application Ser. No. 06/792,210, filed Oct. 28, 1985, entitled "METHODAND APPARATUS FOR PRODUCTION OF INVOLUTE GEAR TOOTH FLANKS" now U.S.Pat. No. 4,811,528, granted March 14, 1989, and to the commonly assignedU.S. Application Ser. No. 07/002,224, filed Jan. 12, 1987 and entitled"Apparatus for Production of Involute Gear Tooth Flanks"now U.S. Pat.No. 4,815,239, granted March 28, 1989.

BACKGROUND OF THE INVENTION

The present invention broadly relates to a method for fabricatinginvolute gear tooth flanks.

Generally speaking, the invention relates to a new and improved methodfor fabricating involute gear tooth flanks without or with geometriccorrections by means of at least one machining tool and in which methodmachining, feed and traversing motions between the machining tool and aworkpiece or gear blank are performed.

The invention is also concerned with a machine tool or machiningapparatus for performing the method and comprising on this machineframe. The machine tool or machining apparatus further comprises aworkpiece or gear blank carrier or support and clamping means forholding a workpiece or gear blank and a multiple-carriage orcarriage-and-slide arrangement for performing the machining, traversingand feed motions. Drive means as well as control means for carrying out,i.e. controlling and powering, these movements are also provided.

In a known method of fabricating involute gear tooth flanks, conical ordished grinding wheels are used which each respectively process a rightand a left gear tooth flank. For this purpose, the two grinding wheelsare fixed at an angle in relation to each other such that working ormachining planes of the grinding wheels define the surfaces of ahypothetical generating rack on which the gear to be ground is generatedor rolled. The inclination of the grinding wheels to a normal to thegenerating roll plane or pitch plane is generally the same as thepressure angle o of the gear teeth. The relative motion between themachining tool or grinding wheel and the workpiece or gear blank forgenerating the involute form, the so-called generating roll motion, isderived from the pitch circle. FIG. 6 hereof shows the generatingprocess of a gear wheel on a hypothetical rack in transverse section andin a number of phases. The points A, P, C, T and E delimit segments ofthe line of action which correspond to regions of the tooth flank. Theaddendum flank or flank region is formed on the tooth flank during thegrinding process when the section AC of the line of action is traversed.When the section CT of the line of action is traversed, then an initialor outer dedendum flank or flank region of the tooth flank involute iscorrespondingly formed.

The point T on the line of action is reached when the corner point K ofthe basic tooth rack profile lies on the line of centers OC connectingthe workpiece or gear blank center 0 with the pitch point C on the lineof action. The section TE of the line of action corresponds to twosegments on the tooth flank which are formed simultaneously (cf. FIG.11): a further or inner dedendum flank portion of the tooth flankinvolute and a trochoidal or undercut dedendum or root fillet radius.The point E is the lowest or innermost point of the involute and at thesame time the initial point of the dedendum or root fillet trochoid orundercut. The curves or semicircles shown in dotted lines in FIG. 11indicate which points of the inner dedendum flank portion of the toothinvolute and of the dedendum fillet or undercut are simultaneouslygenerated.

FIG. 16 shows the working or machining points Pi', Pi" on a dished orflat grinding wheel or disk which is in contact with the tooth flank ofthe workpiece or gear blank. During the grinding process, these workingor machining points wander, depending upon the generating roll positioni, along the machining or grinding surface of the disk and the edges ofthe grinding wheel and each such working or machining point lies on ageneratrix of the tooth flank surface.

During the generating process, a working or machining point of a conicalor beveled grinding wheel will wander along a meridian over a working ormachining width of the grinding disk corresponding to the entire toothflank. Machines or apparatus for such a process are, for example,described in the Swiss Pat. No. 592,604 granted Oct. 31, 1972, and theGerman Pat. No. 2,050,946, granted May 13, 1976. It is a disadvantage ofthis process that topological or geometric flank corrections can only becarried out to a relatively limited extent since due to the forces whicharise between the workpiece or gear blank and the machining tool andother system conditions relative to the size of the gear tooth ingeneral, a larger area of the grinding wheel or disk is involved in themachining process producing the involute form. The working or machiningregions especially can only be very coarsely localized and can beinfluenced only by altering system features which are very difficult orimpossible to carry out, such as grinding wheel size or shape.

SUMMARY OF THE INVENTION

Therefore, with the foregoing in mind, it is a primary object of thepresent invention to provide a new and improved method for fabricatinginvolute gear tooth flanks which do not exhibit the aforementioneddrawbacks and shortcomings found in the prior art.

Another and more specific object of the present invention is to assurethat the working or machining regions of the grinding wheels can, on theone hand, be kept small and that working or machining points of grindingwheel surfaces can, on the other hand, be predetermined in location forachieving more accurate tooth flank forms and more accurate and specifictopographical or geometric corrections.

Now in order to implement these and still further objects of theinvention, which will become more readily apparent as the descriptionproceeds, the method of the present invention for fabricating involutegear tooth flanks is manifested by the features that working ormachining contact between the workpiece or gear blank and the machiningtool or grinding wheel is confined to a selectable working or machiningpoint or to within the immediate vicinity thereof. The feed motion isperformed such that the working or machining point is guided essentiallyalong a selectably predeterminate working or machining line which liesat least approximately on the tooth flank surface for generating ageneratrix envelope.

The apparatus of the present invention for fabricating involute geartooth flanks is manifested by the features that it comprises guidingmeans and control means for controlling and guiding a selectable work ormachining point on machining line essentially extending along the toothflank surface. For this purpose, the guiding means are connected withposition determination means which transmit positioning signals to thecontrol means for controlling the driving means.

An advantageous step of the inventive method consists in that thevariably selectable working or machining point of the tool or grindingwheel, or at least a region in the immediate vicinity of this machiningpoint, is confined during the machining operation by a supplementaryfeed motion of the tool to a working or machining region of themachining tool which is prescribable or predeterminate independently ofthe generating process.

A further advantageous step of the method consists in that theselectable working or machining point of the machining tool, or at leasta region in the immediately vicinity of the machining point, is confinedduring the machining operation conjointly by a supplementary feed motionof the machining tool and a supplementary feed motion of the workpieceor gear blank toward the machining tool to a working or machining regionof the machining tool which is prescribable or predeterminateindependently of the generating process.

The supplementary feed motion of the machining tool can be performedalong a symmetry plane or surface of a tooth space.

The supplementary feed motion of the workpiece or gear blank towards themachining tool can also be performed as a translatory motion, a rotarymotion or a pure generating feed motion.

According to a further advantageous method step, the selectable workingor machining point of the machining tool, or at least of a region in theimmediate vicinity of the machining point, is continuously andprescribably or predeterminately displaced within the working ormachining region during the machining operation by means of a work ormachining point feed motion conforming to the wear of the machiningtool.

The supplementary feed motions can be coupled with conventional or basicfeed motions performed along the working or machining line forgenerating involute gear tooth flanks according to their generatrixenvelopes.

For this purpose, the prescribable or predeterminate, i.e. selectablypredeterminate, working or machining line may comprise segments which atleast approximate generatrices of the tooth flank surface.

The prescribable or predeterminate, i.e. selectably predeterminate,working or machining line can also be composed of segments in which afirst branch at least approximates a generatrix and a second branch atleast approximates a profile line.

Furthermore, it is also possible to couple the supplementary feedmotions with the conventional or basic feed motions along the working ormachining line for producing involute gear tooth flanks according totheir flank generatrix or tooth trace envelopes.

The prescribable or predeterminate working or machining line can becomposed of segments which at least approximate tooth traces or flanklines of the tooth flank surfaces.

Alternatively, the prescribable or predeterminate working line can becomposed of sections or segments in which a first branch is at least onetooth trace or flank line and a second branch or segment at leastapproximates a profile line.

The supplementary feed motion can be performed tangentially to the toothflank or tangentially to a tooth flank meridian.

A further possibility is that the control of the working or machiningpoint relative to the machining tool or grinding wheel surface can beperformed in dependence of wear measurements on this machining toolsurface.

The control of the motion of the work or machining point for achieving abetter exploitation of the machining tool can also be performed independence of wear measurements and empirical values.

Furthermore, it is advantageous if the motion of the work or machiningpoint is continuously or discontinuously superimposed on thesupplementary feed motion.

In this inventive method, traversing motion for generating uncorrectedtooth flanks can be performed in at least one stage, i.e. in one or morestages.

In the generation of topographically or geometrically corrected toothflanks, the traversing motion on the selectably prescribable working ormachining line can be performed in at least one stage. The traversingmotions of possible further stages corresponding to the correctionvalues for each correction point are performed continuously.

The traversing motions can be performed either by the machining tool orby the workpiece or gear blank and, here again, can be purelytranslatory, purely rotary or a combination of both types of motion.

All motions can be controlled by prescribable or predeterminate data orfunctions of data.

However, it is also possible for all motions, except generating feedmotions known per se, to be controlled by prescribable or predeterminatedata or functions of data.

The supplementary feed motion can also be controlled such that, givenvariable and continuously measured values for the generating path of theworkpiece or gear blank center and for the longitudinal feed of themachining tool or grinding wheel relative to a reference point on thehypothetical reference or basic generating rack tooth flank tangentsurface, the distance of the common working or machining point of themachining tool and of the workpiece or gear blank from a referencepoint, for example from the reference point on the reference or basicgenerating rack tooth flank, at least approximately satisfies theequation:

    ys=h·tan γ+(w·sin αt)/cosγ (1)

The means of guidance of the apparatus for carrying out the method cancomprise at least one slide or carriage providing at least onesupplementary degree of adjustment freedom for the motion of themachining tool or tools.

One slide or carriage can also be provided for each machining tool as aguide means so that the machining tool or tools and their associatedworking or machining point are, in addition to all other motions, alsodisplaceable tangentially to the tooth flank surface.

At least one slide or carriage can be provided as a guide means for afeed motion of the machining tool radial to the workpiece or gear blank.It is also possible to provide a slide or carriage for a feed motiontangential to the gear tooth flank.

Furthermore, the control means for controlling the generating feedmotion can be mechanical means of control known per se, while thecontrol means for controlling all other motions, or for that matter allof the motions, can be electronic circuitry means.

It is especially advantageous for the electronic circuitry means tocomprise a master computer or control processor connected to:

a master control interface for signal input and output;

a grinding wheel control means for regulatably controlling at least onegrinding wheel drive means;

a carriage control means for conjointly controlling appropriate drivemeans for standard pressure angle, tooth helix angle and motion of theintermediate slide or carriage to adjust or regulate the pressure angleadjustment;

an adjustment means for adjusting the tooth helix angle and at least oneintermediate slide or carriage;

supplementary feed control means for controlling at least one drivemeans for at least one supplementary feed motion of each machining tool,for example either by means of a slide or carriage or as a resultant ofa number of conjoint feed motions;

a traversing control means for controlling at least one drive means fornormal traversing motions, topographical or geometrical correctiontraversing motions or both; and

a measuring control means for operating a grinding wheel measuring ormonitoring means and also connected to the control means for controllingthe other motions.

The machining tool can comprise a dished grinding wheel or disk of atype known per se, a conical or beveled grinding wheel or disk of a typeknown per se or a dished frustum of a cone with an included or coneangle slightly less than 180° .

An important advantage of the inventive method consists in that, even incomparison to the topographical or geometric correction relationships,larger and therefore more stable grinding wheels or disks or also othertypes of machining tools, for instance milling cutters, can be employed.This also entails other economical and technological advantages. Inparticular, in comparison to known methods, only a relatively small zoneof the grinding wheel or disk need be sensed for wear monitoring andmeasurement. The controllable displacement of the active grinding zoneentails, among other things, the additional advantage of an improvedself-sharpening effect and therefore a considerably better exploitationof the grinding wheel or disk. The working or fillet radius cantherefore also be controllably and considerably improved and machined.

The adjustability of the grinding wheel or disk is also improved due tothe improved controllability of the active machining zone or region ofthe grinding wheel or disk as a result of its working or machiningregion being reduced in size and of the controllable displacement of theworking or machining point. The topographical or geometric correctionscan also be carried out considerably more accurately and with betterdistribution by means of such a controllable and practically definableworking or machining point. The end or final values as well as controlvalues for geometric correction are more easily mastered and betterrealizable, or are only thus possible. Difficult running properties ofgears can be mastered and corrected considerably more specifically andtherefore better than hitherto. The accuracy of fabrication is betterand therefore better suited to specific conditions. There thus results aconsiderable improvement in the quality of the finished gears.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood and objects other than those setforth above will become apparent when consideration is given to thefollowing detailed description thereof. Such description makes referenceto the annexed drawings wherein throughout the various figures of thedrawings there have been generally used the same reference characters todenote the same or analogous components and wherein:

FIG. 1 shows the geometric relationships between a helical spur gear andthe associated reference or basic generating rack tooth flank in a firstgenerating position;

FIG. 2 shows the geometric relationship between a helical spur gear andthe associated reference or basic generating rack tooth flank in asecond generating position;

FIG. 3 shows the projection of the reference or basic generating racktooth flank on the transverse section plane in two generating positions,including the geometrical relationships of significant variables;

FIG. 4 shows the projection of the reference or basic generating racktooth flank on the transverse section plane and, superimposed thereupon,a rotation of the reference or basic generating rack tooth flank intothis transverse section plane, including the geometrical relationshipsof significant variables;

FIG. 5 shows a projection of the reference or basic generating racktooth flank according to FIG. 4, including significant geometricalvariables and relationships for two generating positions;

FIG. 6 shows the gear generating relationships between the gear toothflank and the machining tool surface in various generating positionsaccording to the state of the art;

FIG. 7 shows the gear generating relationships between the gear toothflank and the machining tool surface in various generating positionaccording to the invention;

FIG. 8 shows a variation of working or machining lines for processing oftooth flanks extending essentially along generatrices;

FIG. 9 shows a further variation of working or machining lines extendingessentially along helices or spiral lines;

FIGS. 10a, 10b and 10c show various grinding wheels suitable for theinventive method;

FIG. 11 shows simultaneously generated points of the second or innerdedendum portion of the tooth flank involute and the root fillet radiusor undercut;

FIG. 12 shows a depiction of the important motion axes of the inventivemethod when using a work or machining line comprising generatrixsegments wherein, for the sake of representational clarity, therelationships for fabrication of straight toothing are shown;

FIG. 13 shows a schematic diagram of a control device or means for anexemplary embodiment of a machine tool or gear generating machine;

FIG. 14 shows a schematic depiction of an exemplary embodiment of amachining tool or gear generating machine employing a working ormachining line having generatrix linear segments;

FIGS. 15a and 15b show the schematic depiction of a further exemplaryembodiment of a machining tool or gear generating machine employinghelical or spiral working or machining lines; and

FIG. 16 shows the two working or machining points of prior art methodswhen employing a generatrix working or machining line and using a dishedgrinding wheel.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Describing now the drawings, it is to be understood that to simplify theshowing thereof only enough of the apparatus for fabricating involutegear tooth flanks has been illustrated therein as is needed to enableone skilled in the art to readily understand the underlying principlesand concepts of this invention. In one exemplary embodiment of theinventive fabricating method for involute gear tooth flanks, theworkpiece or gear blank is in general horizontally or vertically clampedon a workpiece or gear table or rotary table equipped for performing therequisite generating feed motions. The tooth flank is subjected to agenerating roll motion in relation to a machining surface of at leastone grinding wheel or disk and which machining surface corresponds tothe tooth flank of the reference or basic generating rack profile. Thegrinding wheel or disk simultaneously performs a rotary slide orcarriage motion and a feed motion essentially along a generatrix of thetooth flank as a working or machining line. A traversing motion in thedirection towards the tooth flank (i.e. a feed motion) determines thedepth of cut. The workpiece or gear blank performs the generating feedmotion (generatrix envelope).

In addition to these feed motions, a supplementary feed motion isperformed which is tangential to the tooth flank, preferably tangentialas seen in transverse section (cf. FIG. 7). This supplementary feedmotion is a relative motion between the workpiece or gear blank and themachining tool or grinding wheel or wheels. The grinding wheel or diskis thus entrained together with its momentary or active and variablyselectable working or machining point in the direction of the gear toothflank and the prescribable or predeterminate and selectable working ormachining point moves on the tooth flank along a generatrix as aselectable or selectably predeterminate working or machining line, alsoknown as the operative line. The working or machining point on thegrinding wheel or disk remains (except for its rotation) at one pointand does not wander, as is the case with prior art methods, over theentire working or machining width of the grinding wheel or disk incorrespondence to the generating motions of the tooth flank on it. Theworking or machining point on the grinding wheel or disk is thusprescribable or predeterminate and selectable.

Furthermore, it is held in a prescribable working or machining region ofthe grinding zone independently of the grinding process. Consequently,this working or machining region can also be of smaller dimension orextent than in prior art methods. This is especially advantageous withcoated tools, since the coating can then be applied to a smaller area.In particular, the supplementary feed motion can be controlled orgoverned in accordance with the formula or equation (FIG. 5):

    ys=h·tan γ+(w·sin αt) /cosγ (1)

wherein:

ys=distance of the working or machining point S from a contact point Mon the gear tooth flank;

w=generating path length; continuously

h=grinding stroke length; monitored

αt=pressure angle in transverse section; and

γ=angle between generatrix and pitch line of the generated tooth flank.

Turning now specifically to FIG. 5 of the drawings, a helical spur gearis seen in mesh with a hypothetical reference or basic generating rack.In the initial position of the generating roll motion and the grindingmotion, the contact line between the reference or basic generating racktooth flank and the gear tooth flank is the line Bo and a working areaor machining region meridian is the dotted line To. Consequently, theworking or machining point is the intersection point S of these twolines. As is depicted in FIGS. 3 and 5, the distance q between thecontact line Bo and a contact line B corresponds to the generating pathw and is related thereto according to the formula:

    q=w·sinαt                                   (2)

Consequently, during a generating path w and a grinding stroke h, theworking or machining point wanders towards S. The distance ys of point Sfrom an initial position M (chosen as reference point and advantageouslyas median point of the developed flank plane, i.e. of the generatingrack tooth flank) is calculated according to formulas given above. Thissupplementary feed motion, e.g. of the grinding wheel or disk, can besuperimposed on a work or machining point motion which discontinuouslyor continuously incrementally prescribably displaces the work ormachining point relative to its working area or machining region.Therefore, the working or machining point, for example during a givennumber of grinding wheel revolutions, can be held at a specific distancefrom the inside or the outside edge of the working or machining surfaceof the grinding wheel and subsequently brought into an adjacent positionfor the following revolution group (displacement cycle) until the wholeor a prescribable or predeterminate portion of the working area ormachining region of the machining tool, i.e. of the grinding wheel, hasbeen swept. Subsequently, a new displacement cycle of the grinding wheelis initiated. With this continuous prescribable or predeterminate pathis swept or traversed in the working area or machining region duringeach displacement cycle. Nevertheless, it is not absolutely necessarythat this work or machining point displacement be performed in acyclical manner. It is also possible to jump from one circular track orpath to another circular track or path.

The control of working or machining point displacement is performedaccording to prescribable or predeterminate conditions or values. Thesevalues or conditions are stored in any desired form on a data carrier,for example in the form of a curved guide template or as a cam guidedisk, in the form of a measuring point or pulse regulation by sensingthe machining tool or grinding wheel for signs of wear or itsoptimization or for better tool exploitation, or in the form of a pulsegenerator, an electronic data carrying medium, mass memory or the like.Especially the latter, either by themselves or in conjunction withmeasuring point regulation, can contain empirical values which have beenfound to produce optimal flank surface properties.

The traversing feed motion is carried out in a manner known per se whengrinding gear tooth flanks without topographical or geometriccorrections. If the case should arise that a tooth flank is to be groundwith a topographical or geometric correction, i.e. with a profile whichvaries over the width of the tooth, then either the correction motion issuperimposed on the feed motion or a correction motion issupplementarily, i.e. entailing more than one step, performed. This isessentially a question of control depending on which value is taken as areference value, respectively as an initial value, for the feed motion.It is necessary to fully traverse in each correction point from thisreference value in a single step or a number of steps. The assignment ofthe correction values to the individual points of the tooth flank isknown per se and is preferably done in a coordinate system of the fieldof action or machining engagement. Either the workpiece or gear blank orthe machining tool or grinding wheel can perform the traversing motion.

The working or machining line of the embodiment of the methodhereinbefore described can take the form of a zig-zag line whoseindividual segments each extend essentially along a generatrix of thetooth flank (cf. FIG. 8). In practice, however, the actual working ormachining line will always deviate somewhat from the theoretical workingor machining line. When using this working or machining line workpiecesor gear blanks, the tool or grinding wheel performs a continuousgenerating feed motion. In addition, the machining tool or tools aremoved along the surface of the tooth flank with an oscillating orstroking feed motion. Another form is a meandering or wandering type ofwork or machining line in which the working or machining point is guidedalong a generatrix, or at least approximately along a generatrix, as onebranch of the segment during a stroke or stroking feed motion. Forchanging or switching over from one generatrix to a generationallyrelevant adjacent generatrix, the working or machining point is guidedalong a profile line, possibly a tooth or flank line as a second branchor segment of the working or machining line. This depends on theposition of the turning or reversing point relative to the tooth flankin the course of motion of the grinding process. A discontinuousgenerating feed motion of the workpiece or gear blank or a correspondingmotion of the machining tool or tools results from this configuration ofthe working or machining line when the machining tool or tools moveabout the stationary workpiece or gear blank. In this way the machiningtool or tools perform the supplementary stroke or stroking feed motion.

In a further embodiment of the method for fabricating involute geartooth flanks, the workpiece or gear blank is, as usual, clamped to awork or machining table which rotated and either the work table or themachining tool or tools are moved in accord therewith in the directionof the axis of the gear, then the working or machining point isdisplaced along a working or machining line in the form of a helical orspiral zig-zag line on the tooth flank (tooth trace or flank lineenvelope). The generating feed motion, the rotary motion and the axialfeed motion are to be carried out such that they are mutually adapted toor match each other so that the working or machining point always lieson the tooth flank. Therefore a helical or spiral motion is superimposedonto a generating motion. The grinding wheel or disk carries out asupplementary feed motion whose direction of motion lies in the workingor machining plane or surface of the grinding wheel or disk, i.e. liesin a tangential plane of the tooth flank, so that the selectable workingor machining point or its immediate vicinity (the size of which dependson the form of the grinding wheel) is essentially always guided alongthis working or machining line.

The control of these motions can be the result of a combination ofelectro-mechanical control utilizing known means, for example forgenerating the generating feed motion, and of individual motor drivemeans, in which appropriate position sensors are connected to theregulating and control circuits. It is, however, also possible tocontrol these movements purely electronically with the reference valuesstored on the most various forms of data storage medium, for examplemechanical data storage media such as cam discs or template bars etcetera, magnetic data storage media, optical data storage media etcetera and, by means of the appropriate means for reading-out andtransmission and control, to transmit these values to the drive means.

Discontinuous control of the generating feed motion or increments. Theworking or machining point is guided along a helical or spiral line ofthe tooth flank and in the region of the flank end an incremental switchor change movement is undertaken in the form of a generating feed motionwhich permits the subsequent generatrix envelope to occur. In this way,one generatrix envelope is juxtaposed with another generatrix envelope.The generating feed motion can be performed either by the workpiece orgear blank or by the at least one machining tool or grinding wheel. Theworking or machining line then has a meandering course or path and itssegments consist of two branches: a tooth trace or flank line and aprofile line. Consequently, the profile line will, in general, lie onthe virtually extended tooth flank, i.e. outside the gear tooth flank.The supplementary generating feed motion of the machining tool must beperformed in accordance with the incremental feed motion, i.e. thegenerating motion, in order that the working point, despite theincrementation, be maintained in the same position relative to ' theworking or machining surface of the machining tool, i.e. the grindingwheel or disk.

If it is required that the working or machining point be continuously ordiscontinuously displaced within the working area or machining region ofthe machining tool in order to achieve a uniform wear of the machiningtool or to adapt the wear of the machining tool to the economic factorsof the machining operation, i.e. to optimize machining tool wear inrelation to the machining operation, then a further working or machiningpoint motion is performed. This can be superimposed on the supplementaryfeed motion or can be undertaken separately from it. The variablyselectable working or machining point, also called the operative point,is displaced relative to the machining tool on its working or machiningsurface, i.e. on the effective cutting area or region of the grindingwheel. This can be achieved continuously according to a spiral line,discontinuously by circular lines or possibly via random number controlin order to achieve the most uniform and patternless wear possible ofthe grinding wheel or disk.

This further embodiment of the inventive method also allowstopographical or geometric correction traversing motions to be performedin addition to the normal traversing motion. These correction motionscan be controlled in a known manner from the field of action or ofmachining engagement and ' can be performed either purely rotationallyor translationally by the workpiece or gear blank as well as by themachining tool or grinding wheel.

A further motion can be performed in each of the embodiment of themethod, namely the generally noncontinuous adjustment of the toolsupport by a variation amount of the helix angle β of helical teeth.This adjustment makes possible, especially when employing dishedgrinding wheels or disks of conventional construction, a substantialreduction of the circumference of the working or machining point toalmost exactly a point. This motion, just as the other motions, can alsobe performed by a control program. Here, too, the program can be storedon mechanical or magnetic storage media and can be brought into serviceby means of appropriate data transmission means, for instancemechanical, optical, electrical or magnetic means.

Depending on the working line, a different generatrix envelope networkresults from each of these embodiments of the method. This generatrixenvelope profile network can be optimally configured by means of anappropriate adjustment or matching of the feed and traversing motionswith respect to the corresponding variables.

If methods with helical or spiral working lines are employed, or ifmethods with helical or spiral lines which consist of various componentsegments are employed, then there results the important advantage thatthe tool support or head of the machine tool or gear cutting machine ismoved not along an inclined straight line but rather along a vertical.Consequently, the machine is not loaded by the displacement of theweight of the tool head, a load which may be quite considerabledepending on the operating speed. This contributes substantially to thefabrication accuracy of the workpieces or gears.

It represents an important advantage if the correction traversing motioncan be performed by the machining tool, since workpiece or gear blankmotion is then saved. In this way the stability of the machine can besubstantially increased and vibrations can be avoided.

Depending on the application, in the embodiment of the method withhelical or spiral component segments for the machining line, thegeneratrix envelope can be controllably concentrically orquasi-concentrically altered, on the one hand, and controlled in width,on the other hand. In particular, the generatrix envelope widths in theregion of the tooth head or addendum and the tooth root or dedendum canbe carried out in different widths.

If only simple dedendum or addendum a normal corrections are to beperformed, then they can be generated when employing the tooth trace orflank line envelopes by means of simple relative motions. In principle,the calculation and execution of flank corrections is simpler in thiscase, since the envelopes of tooth trace or flank lines are limited. Forexample, the same values are used during a complete grinding stroke innormal profile corrections. With the choice of appropriate values forthe correction parameters, profile corrections can also be generated bytangential motions. It is also basically possible to make use ofcorrected tools, for example grinding wheels or disks or milling face orside cutters. Slot milling cutters or end mills or the like can also beused. Analogously, the same values are always set for each envelope whenperforming longitudinal corrections.

In each of the described exemplarily embodiments of the inventivemethod, that is with a generatrix machining line and with helical orspiral component segments in the working or machining line, it isadvantageous that topographical or geometric corrections can beperformed much more accurately than heretofore, since they are generatedusing practically a single working or machining point and the desiredcorrection values are freely prescribable. Furthermore, grinding wheelswith flat or conical working or machining surfaces can be used. Theseworking or machining surfaces are easily produced and maintained.

The choice between both variations of the method will be made accordingto the individual application. If, for example, it is required that onlyvery small or almost no profile differences should occur between thetooth ends and the tooth center and it is necessary to work with acontinuous generating feed motion, then the method described as thesecond exemplary embodiment and having helical or spiral lines assegments or components of the working or machining line will beparticularly advantageous.

Neither of the two embodiments of the method require tools which arespecific to the workpiece or gear blank and none of them require toolcorrection devices with the associated maintenance and inspection work.

FIG. 14 depicts an exemplary embodiment of a machine tool or gearcutting machine for performing the method of the invention forfabricating a gear wheel 1.0 using generatrices as the working ormachining line. There is provided, as usual, a machine frame 1.1 whichon one side carries a displaceable or translatable generating motioncarriage or slide 1.2 and on the other side across or transverse slideor carriage arrangement 1.3 of a type known per se and which isswivellably mounted for adjusting the tooth helix anlge. A tool support1.4, on which a machining tool or tools, for example grinding wheels ordisks 1.5, are seated or fastened, is fixed to the cross or transverseslide or carriage arrangement 1.3. A correspondingly adjustable feedslide or carriage 1.6 is provided for carrying out the supplementaryfeed motion with which the working or machining point of each of thegrinding wheels or disks 1.5 is guided tangentially to the gear toothflank to be fabricated. Preferably, motion or displacement transducersor other position indicators or sensors 1.7 are provided on all of theslides or carriages. These position indicators or sensors 1.7 areconnected with a control arrangement 2.0 (shown in FIG. 13). Thiscontrol arrangement 2.0 can be either purely electronic or amechanically and electronically operated control means. For example, thegenerating motion can be derived in conventional manner from agenerating tape control means. The drive motors also possess rotaryspeed transducers 2.2 (FIG. 13) which are connected with the controlarrangement 2.0. For the sake of expository simplicity, it will beassumed that the machine tool shown in FIG. 14 contains an electromechanical control means in which the generating tape control means isof a type known per se and therefore not shown in FIG. 14 and also notdescribed in detail here.

Such a control means (cf. FIG. 13) possesses a master computer orcontrol processor 2.3 which contains and runs the basic control program.It is connected with a master control interface 2.4 for controlling andmonitoring each tool support 1.4 as well as the other not particularlymentioned motions such as, for instance, the stroke or stroking feedmotions, the adjustment motion of the tooth helix angle β and itsdeviations from the reference value, positional motion of the workpieceor gear blank as well as other necessary and known movements. Thismaster control interface 2.4 is connected to each of the followingcontrol and monitoring devices:

a grinding wheel control means 2.5 for the grinding wheel or disk;

a carriage control means 2.6 for controlling pressure angle, tooth helixangle and intermediate slide motion;

a supplementary feed control means 2.7 for the supplementary feedmotion;

a traversing control means 2.8 for the traversing motion as well as thenormal cutting or grinding, i.e. machining motion including themachining stroke h and also the normal and topographical or geometriccorrection motions; and

a wear control means 2.9 for the grinding wheel measuring device formeasuring grinding wheel wear and for performing diameter compensationet cetera.

A regulator 2.51 is connected to the grinding wheel control means 2.5and also to a grinding wheel drive means 3.1. A rotary speed transduceror measuring means or system or tachometer 2.2 is connected to thegrinding wheel drive means 3.1 and is also connected to the grindingwheel control means 2.5. This feedback regulation circuit serves foraccurate revolution or speed regulation in cooperation with the othercontrolled motions and machine functions.

The carriage control means 2.6 for intermediate slide or carriagemotion, pressure angle and helix angle is connected to a monitoringarrangement 2.62 for position feedback and a second regulator 2.61 whichis connected on one side to an intermediate slide or carriage drivemeans 3.2 for positioning each of a first or right hand control axisU_(R) and a second or left hand control axis U_(L) of the machine toolor gear cutting machine illustrated in FIG. 12 and on the other sidewith a drive means 3.3 for adjusting the pressure angle α or the toothhelix angle λ or both. The intermediate slide or carriage drive means3.2 is connected to a position indicator or sensor 2.63 which in turn isconnected with the carriage control means 2.6 for controlling pressureangle, helix angle and intermediate slide or carriage motion. The drivemeans 3.3 for adjusting the pressure angle α or the tooth helix angle βor both is also connected to a position indicator or measuring system2.64 (which is not shown in FIG. 8 due to the conical ' grinding wheelsemployed), whose measuring data is transmitted to the carriage controlmeans 2.6 for controlling pressure angle, helix angle and intermediateslide or carriage motion. The reference data for each position aretransmitted to this carriage control means 2.6 by the master controlinterface 2.4 and the carriage control means 2.6 returns its own databack to the master control interface 2.4.

The supplementary feed control means 2.7 for the supplementary feedmotion is also connected through its input and output means to themaster control interface 2.4 and is connected through an input means toa monitoring interface 2.72 for monitoring the positions of thecontrolled components. The supplementary feed control means 2.7 is alsoconnected to a third regulator 2.71 which controls the drive means 3.4for the supplementary feed motion. A position measuring system orindicator 2.73 is connected to this drive means 3.4. The positionmeasuring system 2.73 feeds its measuring data for the supplementaryfeed motion to the supplementary feed control means 2.7.

A monitoring means 2.82 for the end or reversing positions, i.e. themachining stroke h and the working or machining positions of the guidemeans is connected to the traversing control means 2.8 for the normaland the topographical or geometric corrections of the tooth flanks. Afourth regulator 2.81 for the drive means 3.5 of the traversing andcorrection motions of the machining tool or each machining tool 1.5 isconnected to the traversing control means 2.8. This drive means 3.5 canalso cooperate with a machine axis which is associated with a workpieceor gear blank so that the traversing motion is performed by theworkpiece or gear blank 1.0. A position measuring system or indicator2.83 is connected to this drive means 3.5 and transmits its signals tothe traversing control means 2.8 for the traversing and correctionmotions.

The wear measuring control means 2.9 is for controlling, monitoring andprocessing measurement data and is connected to measurement and positionindicator means as well as monitoring means and drive output means. Itcommunicates with the master computer or control processor 2.3 throughthe master control interface 2.4.

All these control means 2.5 to 2.9 communicate with the master controlinterface 2.4 and the master control interface 2.4 exchanges signals ordata with the master computer or control processor 2.3 so that allmotions are interrelated and controlled in accordance with theregulating and measuring data.

In FIG. 12 only the most important machine axes to be controlled areshown. These are: W_(L), W_(R) =two, i.e. left and right hand, branchesor segments of the generating feed motion; rfs=positional axis betweenmachining tool or tools and workpiece or gear blank; U_(TL), U_(TR)=left and right hand traversing axes for machining traverse andcorrection traverse; O_(L), O_(R) =left and right hand axes of thesupplementary feed motions; α_(SL), α_(SR) =left and right hand pressureangle adjustment axes; U_(L), U_(R) =left and right hand intermediateslide or carriage axes; β_(S), Δβ_(S) =tooth helix angle and itsvariations; h=machining tool or grinding wheel stroke.

Grinding wheels or disks are preferably utilized as the machining orgrinding tools 1.5. These can have the well-known basic form which issubstantially that of a dish or disk or that of a double cone, as isshown in FIGS. 10a and 10b. In consequence of the supplementary feedmotion utilized according to the method of the invention, the workingareas or machining regions of the grinding wheel or disk can be keptsubstantially narrower than in heretofore known grinding methods. Aparticularly advantageous form of grinding wheel or disk is shown inFIG. 10c. This type of grinding wheel is a modified dished wheel or diskand possesses instead of a planar working or machining surface a conicalfrustum having an included or cone angle slightly less than 180° . Thisform of grinding wheel or disk unites the advantages of the dished wheelwith those of the conical wheel.

An exemplary apparatus for carrying out the grinding method of theinvention employing a working or machining line with helical or spiralcomponent segments can be very similar to the apparatus hereinbeforedescribed. This apparatus also comprises a machine frame 1.1 which onone side ' carries a displaceable generating carriage or slidearrangement and on the other side a pivotably mounted cross ortransverse slide or carriage arrangement 1.3 known per se for adjustingthe helix angle. However, for the helical or spiral working or machiningline, at least one component or portion of the slide or carriage complexmust be guidable parallel to the axis of the machining tool in a strokefeed motion. For this purpose, a further slide 1.10 in accordance withFIG. 15b or an additional swivel axis 1.11 in accordance with FIG. 15amust be provided between the machine frame 1.1 and one slide orcarriage. Alternatively, the motions are so controlled that theresultant motion is identical with this stroke feed motion. Thedifference lies essentially in the temporal control of the individualmotions for achieving the tooth flank form.

The control of these motions can be most readily realized by means of anarrangement of individual drives or drive means for each motion. Thetooth helix is in this case achieved not through a stroke motion of astroke slide or carriage or a corresponding slide or carriagearrangement performed at an inclination towards the gear axis, but bymeans of a slide or carriage which is displaceable parallel to the gearaxis.

In order to employ the helix or spiral as a component segment of theworking or machining line, the workpiece is rotated on the workpiececarrier or support. Only at the end of the tooth trace or flank line isthe incrementation performed for generating the next envelope of theworkpiece or gear blank by means of the generating drive means utilizingeither an electronically controlled drive means or a conventionalgenerating tape control means.

For carrying out the normal or the topographical or geometriccorrections, control means are provided which cooperate with the drivemeans for the individual motion axes. The operating sequence of themotions is determined by mechanical, magnetic, optical or electricalstorage media. The motions can be carried out such that the correctiontraverses of the machining tool are purely rotary, purely translatory ora combination of the two. To achieve this, the drive means are activatedso that the desired resultant motions arise.

The supplementary rotation or angular displacement of the gear or rotarytable i.e. the work or machining table, amounts to:

    nt=Fk/db                                                   (3)

wherein:

Fk=Flank correction value

db=Base circle diameter

nt=Supplementary motion of the gear or rotary table

The control means for generatrix envelope optimization is also similarlystored on storage media as a sequence of signal sequences cooperatingwith position indicators and can be fed into the control means for theindividual motion sequences. The required freedom of play in the drivecan only be achieved with great difficulty or with great design outlaywhen employing prior art drives. For instance, a double-worm drive wouldbe necessary for the gear or rotary table. With the inventive individualdrive arrangement controlled by command sequences, this play can beachieved very easily.

While there are shown and described present preferred embodiments of theinvention, it is to be distinctly ' understood that the invention is notlimited thereto, but may be otherwise variously embodied and practicedwithin the scope ' of the following claims. ACCORDINGLY,

What I claim is:
 1. A method of fabricating involute gear tooth flankson a machine having at least one machining tool and in which methodmachining motions entailing stroke and operating speed of the at leastone machining tool, feed motions entailing relative movements between agear blank and the at least one machining tool for producing at leastone predeterminate involute gear tooth flank, and traversing motionsentailing further relative movements between the gear blank and the atleast one machining tool for producing a predetermined tooth flankprofile and cutting depth, between the machining tool and a gear blankare performed, comprising the steps of:confining machining contactbetween said at least one machining tool and said gear blank at least tothe immediate vicinity of a selectable single machining point on said atleast one machining tool; performing said feed motions such that saidselectable single machining point is guided substantially along aselectable predeterminate machining line lying at least approximately ona tooth flank surface of a gear tooth of a gear being fabricated fromsaid gear blank for generating a gear tooth flank generatrix envelope;said step of confining machining contact entailing the step of confiningsaid selectable single machining point within a predeterminate machiningregion of said at least one machining tool during machining by means ofa supplementary feed motion; said supplementary feed motion entailingthe step of moving said at least one machining tool in the direction ofsaid gear tooth flank of said gear tooth of said gear being fabricatedand thereby compensating for migration of said selectable singlemachining point in said predeterminate machining region of said at leastone machining tool during said step of performing said feed motions andduring a predetermined stroke of said at least one machining tool; andduring said supplementary feed motion of said at least one machiningtool, guiding said selectable single machining point substantially intangential contact with said tooth flank surface of said gear beingfabricated from said gear blank.
 2. The method as defined in claim 1,wherein:said step of confining machining contact at least to theimmediate vicinity of said selectable single machining point entailsconfining machining contact substantially to said selectable singlemachining point.
 3. The method as defined in claim 1, further includingthe step of:during said step of confining said selectable singlemachining point within said predeterminate machining region of said atleast one machining tool, continuously displacing relative to each othersaid gear blank and said at least one machining tool in order to therebycontrolledly displace said selectable single machining point of said atleast one machining tool within said predeterminate machining region andoptimize machining tool wear during the gear fabricating operation. 4.The method as defined in claim 3, comprising the further stepof:performing wear measurements on said predeterminate machining regionof said machining tool; and controlling said controllable machiningpoint motion in relation to said predeterminate machining region independence of said wear measurements.
 5. The method as defined in claim3, comprising the further steps of:performing wear measurements on saidpredeterminate machining region of said at least one machining tool;acquiring and storing empirical values of wear of the predeterminatemachining region of said at least one machining tool; and comparing themeasured wear obtained from said wear measurements and said storedempirical wear values for displacing said selectable single machiningpoint in said predeterminate machining region of said at least onemachining tool.
 6. The method as defined in claim 3, further includingthe step of:during said step of confining said selectable singlemachining point within said predeterminate machining region of said atleast one machining tool, discontinuously displacing relative to eachother said gear blank and said at least one machining tool in order tothereby displace said selectable single machining point of said at leastone machining tool within said predeterminate machining region and tooptimize machining tool wear during the gear fabricating operation. 7.The method as defined in claim 1, wherein,said involute gear toothflanks have tooth flank meridians; and said supplementary feed motion ofsaid at least one machining tool being performed tangentially to saidtooth flank meridians.
 8. The method as defined in claim 1,wherein:during said step of performing said feed motion such that saidselectable single machining point on said machining tool is guidedsubstantially along said selectably predeterminate machining line lyingon said tooth flank surface and extending at least approximately along agear tooth flank generatrix, said traversing motion for fabricatinguncorrected gear tooth flanks is performed in at least one step.
 9. Themethod as defined in claim 1, further including the steps of:defining,on a predetermined tooth flank profile of said involute gear tooth to befabricated, a predetermined number of correction points at which saidpredetermined tooth flank profile deviates from a desired tooth flankprofile; determining, for each said correction point, a predeterminednumber of associated tooth flank profile correction values indicative ofthe deviation between said predetermined tooth flank profile and saiddesired tooth flank profile; during said step of performing said feedmotion such that said selectable single machining point on saidmachining tool is guided substantially along said selectablypredeterminate machining line lying on said tooth flank surface of saidgear tooth of said gear being fabricated, performing traversing motionsalong said selectable predeterminate machining line in at least one stepfor carrying out correcting machining operations in accordance with saidpredetermined number of tooth flank profile correction values andthereby producing said desired tooth flank profile; and carrying outsaid traversing motions in a predeterminate number of steps andperforming continuously all but the first one of said predeterminatenumber of steps.
 10. The method as defined in claim 9, wherein:said stepof performing said traversing motions along said selectablypredeterminate machining line substantially along which said selectablesingle machining point on said machining tool is guided, entailsselectively moving either one of (i) said machining tool or (ii) saidgear blank for carrying out said correcting machining operations. 11.The method as defined in claim 10, wherein:said step of performing saidtraversing motions along said selectably predeterminate machining linesubstantially along which said selectable single machining point on saidmachining tool is guided, entails exclusively rotating said gear blankabout its axis for carrying out said correcting machining operations.12. The method as defined in claim 10, wherein:said step of performingsaid traversing motions along said selectable predeterminate machiningline substantially along which said selectable single machining point onsaid machining tool is guided, entails exclusively translationallymoving relative to said at least one machining tool said gear blank forcarrying out said correcting machining operation.
 13. The method asdefined in claim 3, further including the step of:superimposing saidsupplementary feed motion and said controlled selectable singlemachining point displacement on said predeterminate machining region ofsaid at least one machining tool.
 14. The method as defined in claim 9,wherein:said step of performing said traversing motion for carrying outsaid correcting machining operations entails selectively carrying outeither one of (i) normal correcting machining operations or (ii)geometric correcting machining operations.
 15. The method as defined inclaim 1, further including the steps of:controlling drive means fordriving said at least one machining tool during said machining motions;controlling displacement means for displacing relative to each othersaid gear blank and said at least one machining tool during said feedmotions and said supplementary feed motion; controlling displacementmeans for displacing relative to each other said gear blank and said atleast one machining tool during said traversing motions; storing in acomputer, predetermined data and predetermined data functions governingsaid machining motions, said feed motions and supplementary feed motion,and said traversing motions; and interfacing said computer with controlmeans for carrying out said steps of controlling said machining motions,said feed motions and supplementary feed motion, and said traversingmotions in accordance with said predetermined data and data functionsstored in said computer.
 16. The method as defined in claim 15, furtherincluding the steps of:storing in said computer, data representative ofmachining tool wear; and during said step of controlling said machiningmotions, said feed motions and supplementary feed motion, and saidtraversing motions, carrying out these controlled motions in accordancewith said data representative of machining tool wear stored in saidcomputer.
 17. The method as defined in claim 15, further including thestep of:storing in said computer predetermined data and predetermineddata functions related to correcting machining operations for producinga desired tooth flank profile during fabrication of said gear from saidgear blank; and during said step of controlling said traversing motions,carrying out these controlled traversing motions in accordance with saidpredetermined data and data functions stored in said computer andrelated to said correcting machining operations.